Light Choices for Starting Plants Indoors

There seem to be new lighting choices for indoor plant growing every year. If you’ve been starting annual flower and vegetable plants indoors you probably learned early on that natural light entering through windows is hardly ever adequate. Some type of supplemental light is essential to produce healthy transplants. But what types of bulbs and fixtures work best? And how much money do I really want to spend on something I’ll use for 8-12 weeks each year?

Fluorescent Lights

Many gardeners use 2 ft. or 4 ft. long fluorescent tubes in a fixture (a.k.a “shop light”). The T number is the tube diameter in 1/8 inch units. The traditional T12 tube (1 ½ in. dia.) has been largely replaced by slimmer T8 (1-inch dia.) and T5 tubes (5/8 inch dia.). All fluorescent tubes give off a small amount of heat– rarely a problem, even when foliage grows into them. Heat from the ballast in the fixture can help hasten germination and plant growth, especially when your set-up is covered with plastic.

PVC light stand

PVC light stand with 4 ft. long T5 fluorescent fixtures. Plants stretch to reach available light.
To produce stocky plants the tubes should be only a few inches from the plant tops.
Photo:  Jon Traunfeld

LED Grow Lights

Light-emitting diodes (LEDs) give off very little heat, use less energy than fluorescent tubes, and last about twice as long. They are also mercury-free and made from plastic so won’t shatter like glass. LEDs appear to be the wave of the future for indoor lighting. Horticulturists and lighting engineers are working worldwide to customize wavelength combinations for specific plant production goals in commercial greenhouses and indoor vertical farms.

But very little research data are available to guide gardener decisions. This is further complicated by the many LED grow light fixtures and systems that are available at widely different prices– most without a track record! The good news is that light and fixture prices are coming down and there are a growing number of “out-of-the-box” options available online and in stores.

Linear LED tubes are available that can replace T8 fluorescent tubes and are about 30% more efficient (and last around 50,000 hours). If you decide to replace your fluorescent tubes with LED tubes be aware that there are four different types- some will work easily with your fluorescent fixture and others require modifications to the fixture.

Tips:

  • For fluorescent fixtures– replace T12 tubes with T8 or T5 tubes (the latter will require a new fixture as well).
  • Gently wipe down any type of light tubes before using them this year to remove dust and grime.
  • LEDs will save you a little on your electric bill but it’s unlikely that the transplants grown will be superior to those grown under fluorescent tubes. So don’t make the switch to LED tubes until your fluorescent tubes are spent.
  • No need to buy special blue or red lights to grow transplants. Whether using fluorescent or LED lighting look for a lumens rating (light intensity) over 3,000 and a color temperature rating (brightness; Kelvin scale) of 5,000 to 6,500 (daylight).
  • Make your own PVC Light Stand
  • More resources for starting seeds indoors

By Jon Traunfeld, Extension Specialist

4 Comments on “Light Choices for Starting Plants Indoors

  1. LED is such an odd source of light. I suppose if the ‘color’ of the (visible) light can be adjusted as easily as it is, it can be adjusted to produce the colors that the plants need, even if no other colors are produced. That is probably why greenhouse that use it have the peculiar pink glow.

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  2. John – great article. Now we need an article on how to measure how much light is coming to our plants, and what units to use (foot candles?).

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    • Light meters are pretty expensive and really not necessary for indoor gardening. The commonly available fluorescent and LED tubes give off enough light for growing healthy transplants.

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  3. Yes, sophisticated growers are using systems with an array of individual LEDs customized for specific plants and specific goals- maximum foliage, large flowers, etc. That pink glow across some agricultural landscapes seems to be increasing.

    Right now, the least expensive LED “natural light” tubes described in the post will suffice for gardeners producing transplants indoors. It’s exciting to see this lighting technology develop!
    Jon Traunfeld

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